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The discovery of high thermoelectric performance in n-type polycrystalline Mg3(Sb,Bi)2 based Zintl compounds has ignited intensive research interest. However, some fundamental questions concerning the anisotropic transport properties and the origin of intrinsically low thermal conductivity are still elusive, requiring the investigation of single crystals. In this work, high-quality p-type Mg3Sb2 and Mg3Bi2 single crystals have been grown by using a self-flux method. The electrical resistivity \r{ho} of Mg3Bi2 single crystal displays an anisotropy with \r{ho} in-plane twice larger than out-of-plane. The low-temperature heat capacity and lattice thermal conductivity of Mg3Sb2 and Mg3Bi2 single crystals have been investigated by using the Debye-Callaway model, from which the existence of low-lying vibration mode could be concluded. Large Gr\"uneisen parameters and strong anharmonicity are found responsible for the intrinsically low thermal conductivity. Moreover, grain boundary scattering does not contribute significantly to suppress the lattice thermal conductivity of polycrystalline Mg3Sb2. Our results provide insights into the intrinsic transport properties of Mg3X2 and could pave a way to realize enhanced thermoelectric performance in single-crystalline Mg3X2-based Zintl compounds.

As a quite unique case a high-temperature modification was previously described for the well-known MoSi2. A detailed reinvestigation, however, proves that even minute amounts of beryllium trigger the formation of a hexagonal CrSi2-type phase rather than the established tetragonal prototype. This ternary MoSi2−xBex is stable at ambient conditions and very likely resembles the high-temperature polymorph of MoSi2. With the help of powder X-ray diffraction, electron backscatter diffraction and energy-dispersive X-ray spectroscopy analyses it was concluded that beryllium replaces silicon atoms in the crystal structure, and that the Be/Si network may contain vacancies.

Half-Heusler phase HoPtSb was studied by means of powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, high-resolution transmission electron microscopy (HRTEM), heat capacity, magnetization, electrical resistivity and magnetoresistance. Measurements were performed in temperature range 2–300 K and magnetic fields up to 14 T. The results revealed significant atomic disorder in the crystal structure of this compound, and indicated that the electrical transport in HoPtSb is noticeably affected by scattering conduction electrons on structural inhomogeneities. Due to large value of the resistivity accompanied by small overall change of resistivity with changing temperature the high-temperature behavior was attributed to disorder-induced violation of the Matthiessen’s rule. In turn, at low temperatures, strong magnetic field of 14 T disclosed resistivity upturn reminiscent of Altshuler-Aronov quantum correction observed in disordered metallic systems.

The carboferrates RE15[Fe8C25] (RE=Dy, Ho) were prepared from mixtures of the elements by arc-melting followed with subsequent annealing at 1373xa0;K. The crystal structures were determined from single crystal X-ray diffraction data and revealed an isotypic relationship to Er15[Fe8C25] (hP48, P321). The main feature of the crystal structure is given by Fe6 cluster units characterized by covalent Fe–Fe bonding interactions. 57Fe Mossbauer spectra of Dy15[Fe8C25] were fitted by three subspectra with relative spectral weights of about 3:3:2 which is in general agreement with the crystal structure. Below 50xa0;K, an onset of magnetic hyperfine fields at the three iron sites is observed which is supposed to be caused by dipolar fields arising from neighboring, slowly relaxing Dy magnetic moments.

Nanostructure of a ThMoB{sub 4}-type (β-type) TmAlB{sub 4} compound, in which YCrB{sub 4}-type (α-type) domains are locally intergrown, is studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Z-contrast images by HAADF-STEM directly represent the arrangements of Tm atoms located at centers of heptagonal atomic columns of B atoms as bright dots, and give us detailed information of intergrowth of type domains in the matrix of the β-type phase, which coherently occurs. Structural and bonding analyses for β-TmAlB{sub 4} point out the closeness in atomic interactions and energy of the α- and β-type structures which support the easy formation of such nanostructure intergrowths. From combination between HAADF-STEM and electronic structure calculation, a detailed local crystal structure with intrinsic building defects is effectively revealed. - Graphical abstract: Nanostructure of a ThMoB{sub 4}-type (β-type) TmAlB{sub 4} compound, in which YCrB{sub 4}-type (α-type) domains are locally intergrown, is studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Z-contrast images by HAADF-STEM directly represent arrangements of Tm atoms located at centers of heptagonal atomic columns of B atoms as bright dots, and give us detailed information of the characteristic intergrowth structure of type domains in the matrix of the β-typemore » phase. - Highlights: • HAADF-STEM images directly represent arrangements of Tm atoms as bright dots. • The α-type planar domains coherently intergrown in the β-type matrix. • Bright strips appear at overlapped regions of Tm hexagons along interfaces between α- and β-type domains.« less

In this work, a new type of lead tungstate crystal (Pb 3 WO 6 ) was synthesized by hydrothermal method under high temperature and high pressure. Crystal structure was characterized by single-crystal X-ray structure determination. Pb 3 WO 6 (monoclinic, P 2 1 / c , (No. 14), a = 7.8643(6) A, b = 9.2036(8) A, c = 9.0652(8) A, β = 90.299(5)°, V = 656.13(2) A 3 , Z = 4) exhibited two different layered arrangements of edge-shared octahedral WO 6 with six oxygen coordination along a axis. Thermal stability was investigated by TG–DSC and two phase transformations were observed at about 647 and 748 °C, respectively. Finally, VUV excitation and emission spectra of Pb 3 WO 6 crystal were studied under the temperature 14 K. The results revealed that samples had weak luminescent properties, which exhibited excitation peak at 285 nm and emission peak at 460 nm at low temperature.

The ternary phase YbNi 1 ± x Ga 2 ∓ x (x ≤ 0.08) has been synthesised from the elements by high-frequency melting in argon atmosphere with subsequent annealing at 600 °C or 800 °C. From X-ray powder and single crystal diffraction investigations the phase is found to be isotypic with MgCuAl2: space group Cmcm, Z = 4, a = 4.0987–4.1147 A, b = 9.8516–9.8620 A, c = 6.5995–6.5916 A for the specimens annealed at 800 °C. The quantum chemical analysis of atomic interactions in YbNiGa2 shows Ga and Ni forming a network polyanion with covalent bonds, while ytterbium cations are located within the cavities of the polyanion. From the magnetic susceptibility data and LIII XAS spectra, the 4f13 electronic configuration of ytterbium (Yb3+) was established in samples with nickel excess (comparing to x = 0), whereas an additional small contribution of the 4f14 configuration is found for compositions with the gallium excess. No change in the ytterbium valence state was detected down to 5 K. In situ low- and high-temperature powder diffraction investigations applying both X-ray synchrotron radiation and neutrons revealed no change in structure within the broad temperature range 3.4–1173 K. Both synchrotron and neutron diffraction data show smooth, but strongly anisotropic variation of lattice parameters below 200 K: the thermal contraction ratio in [100], [010] and [001] directions is 4.5:3.2:1. The temperature dependence of atomic displacement parameters indicates a certain amount of static disorder for all atomic species in the crystal. At least two distinct sites with varying charge distributions in the vicinity of the Ga atoms are confirmed by 69,71Ga NMR spectroscopy.

The lanthanum iron carbide La3.67[Fe(C2)3] was prepared from the elements by argon arc-melting followed by annealing. The crystal structure of the ternary phase was reported previously (space group P63/m with a=878.7(2) pm, and c=535.1(1) pm) [A.M. Witte, W. Jeitschko, Z. Naturforsch. 51b (1996) 249–255]. In the present work the compound was reinvestigated by X-ray powder and single crystal diffraction, and was further characterized by metallographic methods and chemical analyses. Our diffraction data clearly reveal a superstructure with weak superstructure reflections in the space group P63/m with a=879.26(8) pm and c=1604.59(15) pm, thus tripling the previously reported subcell. The crystal structure (refinement to R1=0.044 and wR2=0.075 for 1387 unique reflections and 60 variables) contains Fe(C2)3 trigonal planar groups with the C2 ligands bonded end-on to the Fe atoms. The C–C distance is typical for a double bond. La atoms as the least electronegative component surround the complex anions and form a framework of face-sharing tricapped trigonal prisms. The resulting hexagonal channels at 0, 0, z of the partial structure with chemical composition La3FeC6 are occupied by four additional La atoms per unit cell. These La atoms are fully ordered within a linear chain and display a Peierls-like distortion pattern. However, no long-range order in the a−b plane has been observed due to the random orientation of the chains. Because of the two different orientations which are possible for each chain the situation is similar to an Ising model on a triangular lattice.

The organo-templated iron(III) borophosphate (C{sub 3}H{sub 12}N{sub 2})Fe{sup III} {sub 6}(H{sub 2}O){sub 4}[B{sub 4}P{sub 8}O{sub 32}(OH){sub 8}] was prepared under mild hydrothermal conditions (at 443 K) and the crystal structure was determined from single crystal X-ray data at 295 K (monoclinic, P2{sub 1}/c (No. 14), a=5.014(2) A, b=9.309(2) A, c=20.923(7) A, beta=110.29(2){sup o}, V=915.9(5) A{sup 3}, Z=2, R1=0.049, wR2=0.107 for all data, 2234 observed reflections with I>2sigma(I)). The title compound contains a complex inorganic framework of borophosphate trimers [BP{sub 2}O{sub 8}(OH){sub 2}]{sup 5-} together with FeO{sub 4}(OH)(H{sub 2}O)- and FeO{sub 4}(OH){sub 2}-octahedra forming channels with ten-membered ring apertures in which the diaminopropane cations are located. The magnetization measurements confirm the Fe(III)-state and show an antiferromagnetic ordering at T{sub N}{approx}14.0(1) K. - Graphical abstract: The complex inorganic open-framework of (C{sub 3}H{sub 12}N{sub 2})Fe{sup III} {sub 6}(H{sub 2}O){sub 4}[B{sub 4}P{sub 8}O{sub 32}(OH){sub 8}] consists of borophosphate trimers and iron(III) coordination octahedra arranged to form channels with ten-membered ring apertures in which the organic 1,3-diaminopropane cations are located.

The ternary compound YbNiGa 4 was synthesized from the elements by high-frequency induction melting in an argon atmosphere. No evidence for the existence of a homogeneity range was observed from X-ray powder diffraction data. The crystal structure of YbNiGa 4 was refined using X-ray single-crystal diffraction data: YNiAl 4 type, space group Cmcm, Pearson symbol oC 24, a = 4.0868(1) A, b = 15.2829(5) A, c = 6.5049(2) A, Z = 4, R ( F ) = 0.044 for 255 symmetry independent reflections. The coordination numbers are 19 for Yb, 12 for Ga and 9 for Ni. At ambient pressure, the electron configuration of ytterbium, as derived from magnetisation/magnetic susceptibility and X-ray absorption spectroscopy (XAS) measurements and confirmed by band structure calculations, is intermediate between 4f 13 and 4f 14 . With increasing pressure, the 4f 14 (Yb 2+ ) is continuously converted to 4f 13 (Yb 3+ ).

Crystal structure and thermal expansion of PrGaO3 single crystal, obtained by the Czochralsky method, have been investigated by means of single crystal and high-resolution powder diffraction techniques applying synchrotron radiation in a wide temperature range 12–1253 K. It was shown that PrGaO3 adopts an orthorhombically distorted variant of perovskite structure (GdFeO3 type of structure, space group Pbnm, Z = 4 ) throughout the entire temperature range. Temperature dependence of lattice parameters and respective unit cell volume display anisotropic and nonlinear behavior. Lattice contraction in [010]- and [100]-directions is observed in temperature ranges 12–180 and 12–50 K, respectively. In total PrGaO3 exhibits a negative thermal expansion of the volume between 12 and 50 K. A linear increase of the average bond lengths (PrO)8, (PrO)9, (PrO)12, (GaO)6, as well as the average (OO)8 distances was observed. However, with the average (PrPr)6, (PrGa)8 and (GaGa)6 cation–cation distances a change of slope occurs at 200–300 K. Over all, with rising temperature a decrease of the deformation is observed for the perovskite type structure. A phase transition from orthorhombic to rhombohedral structure of PrGaO3 around 1855 K is predicted from extrapolation of both the temperature dependencies of the (PrPr)6/(GaGa)6 distance ratio and of the experimental temperatures of the R 3 ¯ c –Pbnm phase transition for LaGaO3, CeGaO3 and La1−xRExGaO3 (RE—rare earth) perovskites.

Reaction of potassium hypersilylchalcogenolates (Me3Si)3SiEK (E = S, Se, Te) with organochlorosilanes R4 − xSiClx (R = Me, Ph; x = 1–4) and methylchlorodisilanes (Si2Me5Cl, 1,2-Si2Me4Cl2) yields organosilicon hypersilylchalcogenolates [(Me3Si)3SiE]xSiR4 − x (x = 1–4) and [(Me3Si)3SiE]xSi2Me6 − x (x = 1, 2). A partial substitution product, [(Me3Si)3SiSe]2SiPhCl (2) has been obtained by reaction of PhSiCl3 with 1.5 equivalents (Me3Si)3SiSeK. Besides characterization by 1H, 13C, 29Si, 77Se and 125Te NMR spectroscopy the compounds [(Me3Si)3SiTe]2SiPh2 (1), [(Me3Si)3SiSe]2SiPhCl (2) and [(Me3Si)3SiSe]2Si2Me4(3) have also been analyzed by crystal structure analyses. Starting from (Me3Si)5Si2K treatment with sulfur gave the highly branched potassium heptasilanylthiolate (Me3Si)5Si2SK. Reactions with methylchlorosilanes Me4 − xSiClx (x = 1, 2, 3) yielded organosilicon heptasilanylthiolates [(Me3Si)3Si–(Me3Si)2Si–S]xSiMe3 − x.

Pr 5 Si 3 single crystals have been grown by the floating zone technique with optical heating. The crystals are crack-free, 6 mm in diameter and 40–60 mm in length. Pr 5 Si 3 crystallizes with the tetragonal Cr 5 B 3 crystal structure type (space group: I4/mcm) and with lattice parameters a = b = 7.8172 ( 7 ) A and c = 13.816 ( 3 ) A . Single crystal XRD data have been refined based on the Cr 5 B 3 structure. The electrical resistivity of Pr 5 Si 3 single crystals exhibit metallic behavior with an anomaly at T C = 43.5 ( 1.0 ) K corresponding to a ferromagnetic ordering transition, which was confirmed by magnetic susceptibility measurements.

Ph 2 SiCl 2 and PhMeSiCl 2 react with Li 2 E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE) 3 (R = Ph: 1a – 3a , R = Me: cis / trans - 4a (E = S), cis / trans - 5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE) 2 (R = Ph: 1b – 2b , R = Me: cis / trans - 4b (E = S), cis / trans - 5b (E = Se)) have been observed as by-products. 1a – 5b have been characterized by multinuclear NMR spectroscopy ( 1 H, 13 C, 29 Si, 77 Se, 125 Te). Four- and six-membered ring compounds differ significantly in 29 Si and 77 Se chemical shifts as well as in the value of 1 J SiSe . The molecular structures of 2a , 3a and trans - 5a reported in this paper are the first examples of compounds with unfused six-membered rings Si 3 E 3 (E = Se, Te). The Si 3 E 3 rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te–Te contact of 3.858 A which yields a dimerization in the solid state.

Treatment of 1,2,3-trichloropentamethyltrisilane ( 1 ) with H 2 S/NEt 3 results in the formation of a mixture of two isomers of (Me 5 Si 3 ) 2 S 3 with a bicyclo[3.3.1]nonane ( 2a ) and a bicyclo[3.2.2]nonane ( 2b ) skeleton, while the reaction of 1 with Li 2 Se yields one product only, (Me 5 Si 3 ) 2 Se 3 ( 3a ), with a bicyclo[3.3.1]nonane structure. Besides 1 H, 13 C, 29 Si and 77 Se NMR spectroscopy 3a has also been characterized by a crystal structure analysis. Compounds Si(SiMe 2 EMR 2 E) 2 ( 5a – h : MR 2 : SiMe 2 ( 5a , c , d ), SiPh 2 ( 5b ), GeMe 2 ( 5e , f ), SnMe 2 ( 5g , h ); E=S ( 5a , b , e , g ), Se ( 5c , f , h ), Te ( 5d )) with a spiro[4.4]nonane skeleton have been obtained in mixture with varying amounts of the corresponding six-membered rings (R 2 ME) 3 by reactions of mixtures of 1,2,2,3-tetrachlorotetramethyltrisilane ( 4 ) and diorganodichlorosilanes, Me 2 GeCl 2 or Me 2 SnCl 2 , with H 2 S/NEt 3 , Li 2 Se or Li 2 Te and have been characterized in situ by multinuclear NMR spectroscopy ( 1 H, 13 C, 29 Si, 119 Sn, 77 Se, 125 Te) and GC-MS.

Single crystals of aluminum diboride (space group P 6/ mmm , No. 191) a =3.0050(1) A, c =3.2537 (8) A; Z =1) were prepared by the aluminum flux method. Crystal structure refinement shows defects at the aluminum site and resulted in composition Al 0.894(9) B 2 ≈Al 0.9 B 2 . The defect structure model is confirmed by the measured mass density ρ exp =2.9(1) g/cm 3 in comparison with a calculated value ρ x =3.17 g/cm 3 for full occupancy of the aluminum position. The results of 11 B NMR measurements support the defect model and are in agreement with the structure obtained by X-ray diffraction methods. Electrical resistivity measured on a single crystal parallel to its hexagonal basal plane with ρ (300 K)− ρ (2 K)=2.35 μΩ cm shows temperature dependence like a typical metal. Charge is dominantly carried by holes (Hall-coefficient R =+2×10 −11 m/C). Respective, p-type conductivity is confirmed by theoretical calculations. Chemical bonding in aluminum diboride is discussed using the electron localization function.

1,1,3,3-Tetrachlorotetramethyltrisilane (1b) has been prepared from Ph2MeSiCl and Me2SiCl2 via Ph2MeSiSiMe2SiMePh2 (1a). Reaction of 1b with Li2E (E=S, Se) furnishes the new tricyclic organosilicon chalcogenides (Me2Si)2(MeSi)4E4 (E=S (2a), Se (2b)) with adamantane structures. If a mixture of 1b and Cl2MeSiSiMeCl2 is reacted with H2S/NEt3, (Me2Si)(MeSi)4S4 (3a), a noradamantane with a trisilane and a disilane unit is formed. The molecular structures of 2a and 3a are reported. All new compounds are characterized by NMR spectroscopy (1H, 13C, 29Si, 77Se).

The MnPc(py)2 complex was obtained in the reaction of MnPc with purified and dry pyridine under non-oxidation conditions. It crystallises in the centrosymmetric space group P21/c of the monoclinic system with two molecules per unit cell. The Mn2+ cation is coordinated by four N-isoindole atoms of phthalocyaninato(2−) macrocycle and axially by two nitrogen atoms of pyridine molecules into a tetragonal bipyramid. The MnPc(py)2 crystals are moderately stable under air, but in pyridine solution the MnPc(py)2 complex undergoes oxidation by O2 yieldings the binuclear manganese(III) μ-oxo complex (MnPcpy)2O as evidenced by the UV–Vis spectroscopy. The magnetic susceptibility measurement performed on solid sample of MnPc(py)2 shows the Curie–Weiss behaviour in the temperature region of 300–15 K. The calculated magnetic moment μeff indicates three unpaired electrons (S=3/2), thus the ground state configuration of Mn ion is (a1g)2(eg)2(b2g)1, and the MnPc(py)2 complex is the intermediate spin complex. Below 5.5 K (TN) the magnetic susceptibility sharply decreases due to the cooperative intermolecular antiferromagnetic interactions.

The reaction of a 1:2 molar mixture of 1,2-Me2Si2Cl4 and MeGeCl3 with H2S/NEt3 yielded Me2Si2(MeGe)2S5 (1), the first mixed silicon–germanium chalcogenide with a noradamantane-like structure, while the treatment of a 1:2 mixture of 1,2-Me2Si2Cl4 and PhSnCl3 with Li2Se resulted in the formation of the first silicon- and tin-containing noradamantane Me2Si2(PhSn)2Se5 (2). Both compounds have been characterized by NMR spectroscopy (1H, 13C, 29Si, 77Se and 119Sn). The molecular structure of 1 in the solid state is reported.

The ternary phase Yb4Ni10+xGa21−x has been synthesised from the elements by high frequency melting in argon atmosphere. The homogeneity region has been established from X-ray powder data and confirmed by EDX analysis for 0.3≤x≤1. The crystal structure of Yb4Ni10+xGa21−x has been estimated from X-ray single crystal data: space group C2/m (no. 12), Z=2, a=20.6815(9) A, b=4.0560(4) A, c=15.3520(7) A, β=124.800(3)°, R(F)=0.023 for 1701 symmetry independent reflections with F(hkl)>4σ(F). A special feature of the structure is the local disorder within the gallium/nickel network. Neglecting atomic disorder in the region of the Ga9 and Ga11 positions, the Yb4Ni10+xGa21−x structure is an occupation variant of the Ho4Ni10Ga21 type with nickel atoms partially replacing the Ga atoms in the 2d sites at the centers of distorted icosahedra. From magnetic susceptibility and from LIII-XAS spectra, the valence state of ytterbium is near 3+.

The reactions of 1:1 mixtures of the trisilylmethane HC(SiMe2Cl)3 (1b) and organo Group 14 trichlorides (RMCl3, R=Me, Ph, vinyl (Vi); M=Si, Ge, Sn) with Li2E (E=S, Se) in THF yielded the new bicyclo[2.2.2]octanes HC(SiMe2E)3MR (2a–6b). The products were identified by GC–MS and multinuclear NMR spectroscopy. Trends of the NMR data are discussed. The molecular structures of HC(SiMe2S)3SiMe (2a), HC(SiMe2S)3SiPh (3a), HC(SiMe2Se)3SiVi (4b) and HC(SiMe2Se)3GeMe (5b) are reported.

The first-order phase transition in La 1− x Sm x GaO 3 solid solution perovskite as well as crystal structures of both, room- (RT) and high-temperature (HT) phases, have been studied by means of powder diffraction technique using synchrotron radiation, DTA and DSC analyses. The RT structure of mixed crystals with x =0.10, 0.17 and 0.30 belong to the orthorhombically distorted GdFeO 3 structure type ( Pbnm space group, Z =4), whereas the symmetry of HT La 0.9 Sm 0.1 GaO 3 phase is rhombohedral ( R -3 c space group, Z =6). Transition temperature T c from the orthorhombic to the rhombohedral structure is linearly related to x following T c =422(5)+2599(29) x as a first approximation.

New germanides ScAuGe, TmAuGe, and LuAuGe were prepared by melting mixtures of the elements in an arc furnace and subsequent annealing at 1070 K. The structures of ScAuGe and LuAuGe were refined from X-ray single-crystal diffractometer data: P6 3 mc (No. 186), Z = 2, a = 430.82(5) pm, c = 684.58(10) pm, V = 0.1100(1) nm 3 , wR 2 = 0.0688, 275 F o 2 values, ten variables for ScAuGe; P6 3 mc (No. 186), Z = 2, a = 437.75(4) pm, c = 711.38(6) pm, V = 0.1181(1) nm 3 , wR 2 = 0.0340, 355 F o 2 values, 11 variables, and a batch scale factor of 0.47(3) for LuAuGe. The lattice constants for TmAuGe are a = 439.08(4) pm, c = 716.59(7) pm, and V = 0.1196(1) nm 3 . The crystal structures of these germanides are derived from the CaIn 2 -type structure by an ordered arrangement of Au and Ge atoms at the indium position. The crystal chemistry of ScAuGe and LuAuGe is compared with that of the recently reported cerium compound. Although the AuGe intralayer distances at 259.6 pm in CeAuGe, 260.5 pm in LuAuGe, and 257.6 pm in ScAuGe are similar, the AuGe interlayer distances at 364.2 pm in CeAuGe, 292.7 pm in LuAuGe, and 275.2 pm in ScAuGe differ significantly. Thus, the [AuGe] polyanions are changed from two-dimensional layers in CeAuGe to a three-dimensional network of distorted tetrahedra in ScAuGe. Chemical bonding within the structures was investigated by TB-LMTO-ASA band structure calculations. The energy bands, the densities of states and the valence charge densities are discussed. Bonding is characterized by intralayer bonds between Au and Ge within the puckered AuGe hexagons. In addition, in the case of ScAuGe strong bonds are directed from the Au atoms of one layer to the Ge atoms of the neighbouring layer. Weaker interlayer bonding is observed in LuAuGe and no interlayer interaction in CeAuGe, as already indicated by the pronounced increase of the interlayer distances.

CeAuGe was prepared by reaction of the elemental components in an arc-melting furnace and subsequent annealing at 800°C. Its hexagonal crystal structure (NdPtSb-type) was refined from single-crystal data of an inversion twin: P6 3 mc, Z = 2, a = 446.03(7) pm, c = 793.60(12) pm, V = 0.1367(1) nm 3 , wR 2 = 0.060, 213 F 2 values, 11 variables and BASF= 0.52(3). In the paramagnetic state, the susceptibility of CeAuGe shows Curie-Weiss behaviour above 50 K with μ exp = 2.55(5)μ B and Θ P = −5(1) K. CeAuGe orders ferromagnetically at 10.0(2) K. Its saturation magnetic moment at 5 K is 1.09(2)μ B /Ce. Electrical resistivity measurements show metallic behaviour.

One pot cascade reactions of 3-benzyloxy-cyclohex-2-enone (1) with tert-butyl-(Z)-(+)-2-chloro-3-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]-2-propenoate (2) lead to (1S;2R;5S;7S;8R;4′S)-tert-butyl-2-benzyloxy-8-(2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)-6-oxo-tricyclo[3.2.1.02,7]octane-1- carboxylate (3) and with (E)-(+)-2 to (1R;2S;5R;7R;8S;4′S)-4. The tricyclic compounds 3 and 4 were formed with high diastereomeric excess.

We present a structural model for ordered YBa2Cu3O6.7 on the basis of 545 measured X-ray superstructure reflections of a twinned crystal. The model proposed earlier of a tripled unit cell with two CuO3 chains alternating with one CuO2 chain is verified (Pmmm, a = 11.469(6) A , b = 3.889(2) A , c = 11.720(6) A , Z = 3). Displacements of the strongly scattering atoms Ba and Cu compared to their positions in YBa2Cu3O6.93 are refined.

New salts of the one-dimensional chain-cation (Ag−F)nn+ have been prepared, the structural and magnetic properties of which indicate that they are metallic. A single-crystal X-ray structure analysis of AgFBF4 has established a linear cationic chain, the two Ag−F interatomic distances, at 296 K, being 2.002(3) and 2.009(3) A. Magnetic susceptibility measurements on the poweder from 6 to 280 K show an approximately temperature-independent paramagnetism (χM∼180×10−6 emu mole−1) with no evidence of a Peierls transition in that range. Although the previously known salt, AgFAsF6, has a kinked cationic chain (with, at 166 K, Ag−F−Ag=143.1(1)o, F−Ag−F=175.8(1)o, Ag−F=1.994(2) and 2.001(2) A), it also exhibits temperature-independent paramagnetism from 280 down to 63 K, but a sharp drop in susceptibility below that temperature may signify a Peierls transition. AgFAuF6, which is probably isostructural with AgFAsF6, is similar to it magnetically. The salt AgFAuF4 probably contains a linear cationic chain, since it is isostructural with CuFAuF4, but the salt Ag(AuF4)2, like its relative Ag(AgF4)2, is a magnetically dilute paramagnet, the magnetic susceptibility of which departs very little from the Curie law between 6 and 280 K.

Crystals of YBa 2 Cu 3 O 6.93 were grown in a SnO 2 crucible. Parts of these crystals were untwinned and isolated for X-ray structure investigations at seven temperatures between 103 and 303 K. The positions of the chain atoms Cu(1) and O(4) are occupied at 100 and 93%, respectively. There is no evidence for oxygen atoms between the chains (site O(5) in ( 1 2 0 0) ). The temperature-dependent changes of the lattice constants and the positional shifts of O(1), Cu(2), and Ba are discussed.